According to a first aspect of the present invention there is provided a method of operating an Application Server (AS) that implements an IP Multimedia Subsystem (IMS) supplementary service for a user. The method includes configuring a rule for the user, the rule having an action specifying whether or not an announcement is to be provided and, if an announcement is to be provided, defining media to be used for the announcement. The method further includes determining if a condition of the rule is met by a Session Initiation Protocol (SIP) message relating to the user and, if so, implementing an announcement in accordance with the action.